Question: If $200\%$ of $x$ is equal to $50\%$ of $y$, and $x = 16$, what is the value of $y$?
If $200\%$ of $x$ is equal to $50\%$ of $y$, then $400\%$ of $x$ is equal to $y$. If $x = 16$, then $400\%$ of $x$ is $4x = y = \boxed{64}$.